Stereolithography is an additive manufacturing technology, commonly referred to as 3D printing, that converts liquid materials into solid parts, layer by layer, by selectively curing them using a light source. Stereolithography is widely used to create models, prototypes, patterns, and production parts for a range of industries from engineering and product design to manufacturing, dentistry, jewelry, model making, and education. In addition to stereolithography, 3D printing includes numerous processes, which vary in their method of layer manufacturing, material, and machine technology.
Sacrificial layers of polymers are currently used in stereolithography and micromachining. Sacrificial layers can be made up of acrylic or epoxy polymer resins that are transformed from liquid to solid after exposure to UV light. These sacrificial layers can be made of materials that differ chemically from the structural part being created, allowing selective removal.
In the case of stereolithography, support structures can be created from the same material as the structural part being formed. After the part is cured, the supports are normally removed mechanically, i.e. by cutting and sanding any remaining support, which can make post-processing long and tedious. There is a desire to be able to remove support structures chemically rather than mechanically.
3D-printed preceramic parts tend to be brittle in nature and the mechanical removal of the supports can lead to damage and defects of the part. There is a need to 3D-print preceramic parts with sacrificial structures that can easily be removed without the need to mechanically cut them. There are known formulations that can be used for UV-cured stereolithography, incorporating functional groups that are sensitive to hydrolysis under corrosive (extreme pH) conditions at elevated temperatures. These corrosive conditions may be damaging to the printed part of interest, especially if the part also contains functional groups that are sensitive to hydrolysis.
The introduction of ester functionality along the backbone of the polymer provides a path to hydrolysis—however, this requires etching under caustic conditions (e.g., a sodium hydroxide solution at pH 12). Other polymers that may be used as sacrificial layers in other applications are water-soluble thermoplastics such as polyvinylpyrrolidine (PVP), polyvinyl alcohol (PVOH), polyvinyl acetate (PVA), polyethylene glycol (PEG), and polyacrylic acid (PAA). However, it is difficult to use these polymers in stereolithography without the necessary chemical functionality for UV-based free-radical or cationic curing. For a solid, durable UV-cured support, it is important to have a high density of crosslinking. Even if the polymer backbone is water-soluble, it will usually only swell unless chemical bonds are actually cleaved.
There is a desire for polymers that are soluble in water, rather than organic solvents. Water solubility of a polymer can be enhanced by polymer hydrolysis. Examples of polymers that are susceptible to hydrolysis are polyesters, polyamides, polyurethanes, polycarbonates, polyethers, polyanhydrides, and polyureas, but these all require harsh hydrolytic conditions, making them undesirable.
Thermoplastics are often soluble in organic solvents such as alcohols, ketones, aromatics oils, and hydrocarbons. However, these thermoplastics are not printable in UV-cure-based 3D printing and can damage, craze, or swell traditionally printed polymer components. Some biodegradable polymers, such as those based on lactide, glycolide, and caprolactone, contain hydrolysable ester or carbonate linkages, but these biodegradable polymers are not printable in UV-cure-based 3D printing.
No known prior art provides formulations cured by UV-based free-radical polymerization, cationic polymerization, or hydrosilylation to form 1D, 2D, or 3D structures that can be rapidly hydrolyzed in water. There is a need to create sacrificial layers and structures that undergo rapid hydrolysis and removal, especially for stereolithography of 3D-printed parts, such as (but not limited to) preceramic parts.
Current materials used as sacrificial layers require strongly acidic or basic conditions, high temperatures, or mechanical removal. There are no known stereolithography formulations that allow the rapid, convenient removal of a sacrificial layer by using water alone. There is a commercial desire for radical-curable, cationic-curable, or hydrosilylation-curable resin formulations for producing a sacrificial layer or structure that is easily hydrolysable in water, for quick removal on demand.